全文获取类型
收费全文 | 74973篇 |
免费 | 15252篇 |
国内免费 | 10118篇 |
专业分类
电工技术 | 8658篇 |
技术理论 | 1篇 |
综合类 | 9461篇 |
化学工业 | 1756篇 |
金属工艺 | 1546篇 |
机械仪表 | 5934篇 |
建筑科学 | 1313篇 |
矿业工程 | 1077篇 |
能源动力 | 1500篇 |
轻工业 | 900篇 |
水利工程 | 1139篇 |
石油天然气 | 879篇 |
武器工业 | 1477篇 |
无线电 | 14105篇 |
一般工业技术 | 4712篇 |
冶金工业 | 724篇 |
原子能技术 | 872篇 |
自动化技术 | 44289篇 |
出版年
2024年 | 266篇 |
2023年 | 1590篇 |
2022年 | 3093篇 |
2021年 | 3298篇 |
2020年 | 3347篇 |
2019年 | 2723篇 |
2018年 | 2619篇 |
2017年 | 3032篇 |
2016年 | 3543篇 |
2015年 | 4212篇 |
2014年 | 5501篇 |
2013年 | 5289篇 |
2012年 | 6517篇 |
2011年 | 6805篇 |
2010年 | 5513篇 |
2009年 | 5693篇 |
2008年 | 5948篇 |
2007年 | 6455篇 |
2006年 | 5082篇 |
2005年 | 4257篇 |
2004年 | 3385篇 |
2003年 | 2686篇 |
2002年 | 1990篇 |
2001年 | 1522篇 |
2000年 | 1257篇 |
1999年 | 998篇 |
1998年 | 790篇 |
1997年 | 632篇 |
1996年 | 465篇 |
1995年 | 332篇 |
1994年 | 298篇 |
1993年 | 227篇 |
1992年 | 209篇 |
1991年 | 108篇 |
1990年 | 165篇 |
1989年 | 94篇 |
1988年 | 61篇 |
1987年 | 35篇 |
1986年 | 50篇 |
1985年 | 38篇 |
1984年 | 25篇 |
1983年 | 24篇 |
1982年 | 44篇 |
1981年 | 29篇 |
1980年 | 22篇 |
1979年 | 9篇 |
1978年 | 11篇 |
1977年 | 8篇 |
1975年 | 9篇 |
1959年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 25 毫秒
1.
针对目标估计过程需要大量人工参与、自动化程度低的问题,提出了基于数据质量评价的目标估计方法。利用目标数据质量评价方法,对不同传感器得到的目标数据质量进行科学、有效的测度和评价,并根据质量得分动态调整各数据源在目标估计过程中所占的权重,从而减少人工干预,提高目标估计效能。仿真试验结果证明了该方法的有效性。 相似文献
2.
提出了一种基于FCOS神经网络的小建筑物目标检测算法,针对FCOS模型在特征提取阶段提取到的小建筑物目标特征较少问题,引入多尺度检测和可变形卷积方式,加强网络对小建筑物目标的特征提取能力,并通过改进后的SGE注意力机制降低特征图中的干扰噪声权重。改进后的网络可以提取到更多的小建筑物目标特征,对环境干扰噪声的鲁棒性更强。在自己搭建的数据集上进行了实验测试,结果表明,在相同环境下网络改进后建筑物的整体检测准确率提升了1.7%,其中对小建筑物目标提升了3.6%,减少了小建筑物目标漏检、误检的问题。 相似文献
3.
4.
5.
Aiming at the performance degradation of the existing presentation attack detection methods due to the illumination variation, a two-stream vision transformers framework (TSViT) based on transfer learning in two complementary spaces is proposed in this paper. The face images of RGB color space and multi-scale retinex with color restoration (MSRCR) space are fed to TSViT to learn the distinguishing features of presentation attack detection. To effectively fuse features from two sources (RGB color space images and MSRCR images), a feature fusion method based on self-attention is built, which can effectively capture the complementarity of two features. Experiments and analysis on Oulu-NPU, CASIA-MFSD, and Replay-Attack databases show that it outperforms most existing methods in intra-database testing and achieves good generalization performance in cross-database testing. 相似文献
6.
《International Journal of Hydrogen Energy》2022,47(6):4062-4074
In this work, coupling effects of water content, temperature, oxygen density, and polytetrafluoroethylene (PTFE) loading on oxygen transport through an ionomer thin film on a platinum surface in a catalyst layer of a proton exchange membrane (PEM) fuel cell are investigated using molecular dynamics approach. Taguchi orthogonal algorithm is employed to comprehensively analyze the coupling effects in a limited number of cases. It is found that the effect of operation temperature is the weakest among the four factors, which has the smallest effect index 14.4. Coupling effects including the PTFE loadings on the oxygen transfer through the ionomer thin film is uncovered. Less PTFE loadings should be beneficial for the oxygen transfer. The chemical potential gradient is considered as the major driven force for the oxygen transport through the ionomer thin film, and oxygen density is the dominating factor, significantly affecting the chemical potential in the thin film. 相似文献
7.
《Current Opinion in Solid State & Materials Science》2022,26(6):101024
One of the main challenges in the laser powder bed fusion (LPBF) process is making dense and defect-free components. These porosity defects are dependent upon the melt pool geometry and the processing conditions. Power-velocity (PV) processing maps can aid in visualizing the effects of LPBF processing variables and mapping different defect regimes such as lack-of-fusion, under-melting, balling, and keyholing. This work presents an assessment of existing analytical equations and models that provide an estimate of the melt pool geometry as a function of material properties. The melt pool equations are then combined with defect criteria to provide a quick approximation of the PV processing maps for a variety of materials. Finally, the predictions of these processing maps are compared with experimental data from the literature. The predictive processing maps can be computed quickly and can be coupled with dimensionless numbers and high-throughput (HT) experiments for validation. The present work provides a boundary framework for designing the optimal processing parameters for new metals and alloys based on existing analytical solutions. 相似文献
8.
Farzaneh Khorasani Morteza Mohammadi Zanjireh Mahdi Bahaghighat Qin Xin 《计算机系统科学与工程》2022,40(3):1085-1098
With a sharp increase in the information volume, analyzing and retrieving this vast data volume is much more essential than ever. One of the main techniques that would be beneficial in this regard is called the Clustering method. Clustering aims to classify objects so that all objects within a cluster have similar features while other objects in different clusters are as distinct as possible. One of the most widely used clustering algorithms with the well and approved performance in different applications is the k-means algorithm. The main problem of the k-means algorithm is its performance which can be directly affected by the selection in the primary clusters. Lack of attention to this crucial issue has consequences such as creating empty clusters and decreasing the convergence time. Besides, the selection of appropriate initial seeds can reduce the cluster’s inconsistency. In this paper, we present a new method to determine the initial seeds of the k-mean algorithm to improve the accuracy and decrease the number of iterations of the algorithm. For this purpose, a new method is proposed considering the average distance between objects to determine the initial seeds. Our method attempts to provide a proper tradeoff between the accuracy and speed of the clustering algorithm. The experimental results showed that our proposed approach outperforms the Chithra with 1.7% and 2.1% in terms of clustering accuracy for Wine and Abalone detection data, respectively. Furthermore, achieved results indicate that comparing with the Reverse Nearest Neighbor (RNN) search approach, the proposed method has a higher convergence speed. 相似文献
9.
传统通信模拟系统设计较为复杂,导致模拟过程消耗能量较大,不能准确模拟稳频通信质量。因此,提出基于Matlab的量子激光雷达稳频通信模拟系统。由于振荡器是雷达形成初始信号源的基础,通过分析振荡电路与相位噪声,获得相位噪声函数与通信频率存在的关系;为确保通信过程的稳定,将准确性与稳定性作为信号质量的评价指标,并采用锁频环稳频技术计算频率偏移程度,根据PID控制算法控制频率,量子激光雷达稳频通信;利用Matlab确定激光器、探测器等硬件组成结构,通过时序与数字阵列的设置完成模拟系统设计。仿真结果表明所提系统结构简便、性能稳定,能够真实模拟出稳频通信的信号质量。 相似文献
10.